Lactic acid is a methyl-substituted glycolic acid that has been generated by fermentation of renewable agricultural feedstock resources such as corn, whey, potatoes, rice, cane sugar, beet sugar, molasses of beet-sugar, and the like. Lactic acid is the simplest hydroxyl acid having an asymmetric carbon atom and therefore exists in a racemic form and in two optically active forms.
Two molecules of lactic acid combine to form the monomer (dilactide) for a polymer called polylactic acid, which is a biodegradable and biorenewable material. When dilactide is prepared from racemic lactic acid, the three isomers that result are D-lactide, L-lactide and meso-lactide. The meso isomer can be removed but the D and L-lactide are enatiomers that from the racemic form, rac-lactide, which forms an undesirable amorphous polymer. Most commercial processes use the L-lactide produced from L-lactic acid.
There are numerous uses for lactic acid. It is a common food additive as an acidulant and preservative, and is used in the chemical industry for deliming, metal etching, cosmetic and textile applications, oxychemicals, green solvents, specialty chemicals, and for the production of biodegradable plastics and polymers. Other potential applications include biocompatible polylactic acids for biomedical applications. These polylactic acids have potential applications as prosthetic devices, controlled drug delivery in humans, and food packaging. Additionally, lactic acid may also be used for the synthesis of ethanol resulting in a cost efficient alternative fuel source.
Although some biodegradable polymers are used in medical applications, the vast majority of high-volume consumer plastics continue to be composed of petroleum-based materials, which are essentially nondegradable. Recent events, such as rising costs of petroleum and the environmental costs associated with waste disposal, have made biodegradable polymers economically attractive. The food-processing industry generates large volumes of carbohydrate containing wastes, which are ideal substrates for bioconversion to useful, high-value products, such as lactic acid and its derivatives.
Soybean production is the second largest cash crop in the U. S. behind corn. Most soybeans are used traditionally for soybean meal and oil production. A metric ton of soybeans yields 800 kg of protein-rich meal and 183 kg of oil. The soybean hull, also known as the seed coat, is a byproduct of soybean processing. For every metric ton of soybean processed, about 100 kg of soybean hull is produced which is then disposed of for two American cents per pound. On a dry mass basis, the hulls constitute about 8% to 10% of the total seed, depending on the variety and the seed size. The hull is a hard water-resistant material, which protects the cotyledons and hypocotyls from damage. The soybean hull contains lignocellulose, which is any of several closely related substances constituting the essential part of woody cell walls of plants and consisting of cellulose intimately associated with lignin. Analysis of the soybean hull indicates that it is composed of carbohydrates (80% to 85%), protein (8% to 10%), ash (5% to 8%), and lipids (1%) on a dry mass basis. The dry soybean hull has about 7% to 8% moisture.
The use of microorganisms to generate lactic acid from fermentation of sugars, such as starch, is well known. Various manifestations of the microorganisms have been demonstrated including the use of immobilized and substrate attached microorganisms. For example, lactic acid has been successfully produced from the fermentation of starch carried out by Lactobacillus amylovorous immobilized in porous beads. See Lactic Acid Fermentation From Enzyme-Thinned Starch With Immobilized Lactobacillus amylovorus, Ji Yan, R. Bajpai, E. lannotti, M. Popovic, and R. Mueller, Chem. Biochem. Eng. Q. 15 (2) 59–63 (2001).
U.S. Pat. No. 6,280,985 ('985) issued on Aug. 28, 2001 discloses a process for the separation and purification of lactic acid from a fermentation medium wherein the lactic acid is essentially in the form of a salt or salts. In the process of '985, the lactic acid producing microorganisms are separated from the other components of the fermentation medium forming a salt solution. The resultant solution is acidified to a pH below or equal to 3, and passed over a cation exchange resin to give lactic acid having a fraction with maximum of 25% lactic acid salts (dry weight). This fraction is then subjected to bipolar fractionating electrodialysis, and other purification/concentration techniques.
U.S. Pat. No. 5,932,455 ('455) issued on Aug. 3, 1999 discloses a method for preparing pure lactic acid or salt thereof by fermentation. The preparation process comprises a bioreactor refreshing cycle and a lactic acid production cycle, wherein during the production cycle a solution comprising substantially pure feedstock is recycled though a bioreactor containing refreshed microorganism cells, the lactic acid produced being neutralized by adding an alkali, and the recycling is discontinued when the alkali consumption is substantially diminished. During the refreshing cycle the microorganism cells are refreshed by recycling though the bioreactor a carbohydrate solution enriched with nutrients, thus replenishing the capacity of the microorganisms to produce an acid. Lactate is recovered or converted into lactic acid or other salt.
The use of food-processing waste to produce lactic acid and to simultaneously carry out fermentation and hydrolysis in the production of lactic acid is known. U.S. Pat. No. 6,319,382 issued on Nov. 20, 2001 describes a fermentative production and isolation of lactic acid from a sugar-containing fermentation liquid in a fermentor by means of lactic acid forming bacteria, in which whey protein is present or added as a nutrient substrate for the lactic acid-forming bacteria, wherein at least one protease is added to the fermentor during the fermentation so that hydrolysis of protein to amino acids takes place simultaneously with the fermentation of sugar into organic acid, and wherein lactic acid resulting from the fermentation is isolated from the fermentation liquids. Ammonia is preferably added resulting in the formation of ammonium lactate, and lactic acid is preferably isolated by a process involving ultra filtration, ion exchange, conventional electrodialysis and electrodialysis with bipolar membranes.
U.S. Pat. No. 5,464,760 ('760) issued on Nov. 7, 1995 discloses a fermentation and recovery process for lactic acid production. The method of '760 is used to convert starch to glucose and fermenting the glucose to form lactic acid. The method includes simultaneous saccharification and fermentation through the use of a consortium of bacterial strains. The invention of '760 involves the bioconversion of industrial food waste, such as potato waste, corn, rice, cheese whey, cane sugars, beet sugars or the like, containing starch to lactic acid suitable for conversion to photodegradable or biodegradable plastics. The invention first liquefies the waste using an alpha-amylase enzyme.
Additionally, scientist have successfully used simultaneous saccharification and fermentation to produce lactic acid from cellulose using a combination of Tchoderma reesei as a cellulose for saccharification and Lactobacillus delbrueckii as the lactic acid producing microorganism. See Communications to the Editor: Simultaneous Saccharification and Fermentation of Cellulose to Lactic Acid, Shin-ichiro Abe and Motoyoshi Takagi, Biotechnology and Bioengineering, 37, 93–96 (January 1991).
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.